High-voltage power vacuum fuse

ABSTRACT

A power vacuum fuse for interrupting high-voltage alternating currents. The fuse has one or more fusible, current-responsive elements spanning a pair of spaced, cup-shaped electrodes located with the cavities thereof in facing relationship. The fusible elements extend between and electrically interconnect adjacent edge sections of the sidewalls of the electrodes. Leads to a high-voltage line extend from the central regions of the electrodes, with the base segment as well as the sidewall portions of each being provided with slot means therein extending from the central region to the periphery of the base segment and thence upwardly through the sidewall portion to define a current path to each element which extends both radially outwardly and tangentially with respect to a central axis of the electrodes. The effect of the slotted electrodes is to apply a force to each element which expels it from between the electrodes upon melting and disintegration of all elements, such force having a tangential component which spins the arc established when all the elements are severed. The cup-shaped configuration of the electrodes in conjunction with the slots therein prevents sufficient residue from the elements to be retained between the electrodes in an arc-conducting location and precludes the arc from dwelling at any one point which could cause extreme volatilization of the electrodes so that the circuit will be interrupted at the first natural current zero following severance of the elements.

United States Patent Primary Examiner-Bernard A. Gilheany lnventors Thomas E. Curtis; I

Charles A. Popeck; Lloyd R. Beard, all of Centralia,Mo. [21] AppLNo. 58,922 [22] Filed July28, 1970 [45] Patented Oct. 12,1971 [73] Assignee A.B. Chance Company Csettelie M 7 n [54] HIGH-VOLTAGE POWER VACUUM FUSE 23 Claims, 9 Drawing Figs. s2 U.S.C| 3371278, 337/l6l,337/293 [51] lnt.Cl ..H0lh85/38 [50] FieldofSearch 337/159, H 203,272, 273, 278, 281, 246,461; zoo 144.3 [5 6] References Cited UNITED STATES PATENTS 1,891,111 12/1932 Prince 337/278 3,244,839 4/1966 Albright. 337/278 3,522,399 7/1970 Crgugll ZOO/144B Assistant ExaminerF. E. Bell AttorrreySchmidt, Johnson, Hovey, Williams & Chase AliS TRACT: A power vacuum fuse for interrupting high-voltage altematmg currents. The fuse has one or more fusible,

ponent which spins the are established when all the elements are severed. The cup-shaped configuration of the electrodes in from the elements to be retained between the electrodes in an arc-conducting location and precludes the are from dwelling at any one point which could cause extreme volatilization of the electrodes so that the circuit will be interrupted at the first natural current zero following severance of the elements.

INV/iN'l (ms.

Thomas E. Curtis Charles A. Popeck Lloyd R. Beard flTTORNEYS.

This invention relates to improvements in power vacuum fuses and, in particular, to a vacuum fuse incorporating means for preventing the are established during interruption from causing extreme volatilization of the fuse material.

One of the problems found in vacuum fuses in high-voltage, high-amperage applications is the extreme volatilization of the electrodes and current-responsive element or elements of the fuse when interruption is caused by high short circuit currents. Although a high-vacuum condition may be maintained within the fuse prior to interruption, additional ions are made available to sustain an electricarc if substantial volatilization is permitted to occur at the time of interruption. ManifestlY, complete interruption of the circuitis not effected until the arc is extinguished and, secondly, the prolonged presence of the arc presents a hazard which must be avoided.

It is, therefore, the primary object of this invention to provide a power vacuum fuse which will operate to interrupt high currents at voltages on the order of 600 volts and higher with assurance that an arc will not be long sustained within the fuse at the time that the fusible element or elements thereof are severed by a high short circuit current. As a corollary to the foregoing object, it is an important aim of the present invention to provide a fuse having a pair of facing cup-shaped, slotted electrodes interconnected by a fusible element spanning the distance between adjacent sidewall edges of the electrodes which not only effects rapid movement of thearc upon establishment thereof to prevent the formation of destructive anode spots, but also is operable to expel the residue from melting and disintegration of the element to avoid establishment of an arc-conducting path between the adjacent edge sections of the electrodes.

Furthermore, it is an important object of this invention to provide a fuse as aforesaid having slotted, cupshaped electrodes with a fusible element extending between the edge sections of adjacent sidewall edges of the electrodes, wherein strategically located slots are provided in such electrodes of configuration and in locations to cause the current to apply a force to the element having both radially and tangentially directed components, so that the residue from the element upon melting and disintegration thereof will be expelled from between the electrodes by the force and the are thus established will be moved along the electrodes in a spinning fashion by the tangential force component to prevent the are from dwelling where initially established.

Another important object of the invention is to provide a fuse as aforesaid having a plurality of such current-responsive elements, wherein progressively longer paths for current flow from the central regions of the electrodes to successive elements are provided, and wherein such paths extend both radially outwardly and tangentially with respect to a central axis of the electrodes to effect the application of both radial and tangential force components to the elements.

Still another important object of the invention is to provide a power fuse as aforesaid in which the same components of the fuse construction may be utilized for different ampere ratings, with the exception of only the current-responsive element or elements which may be sized in accordance with the desired continuous current rating.

A still further important object of the invention is to provide a power fuse of the above-described characteristics wherein each of the cup-shaped electrodes has a series of arcuate slots in the base segment thereof which lead into r espeCtive slots extending through the sidewall portion of the electrode to divide the latter into a series of separate components interconnected only in the central region of the base segment so that current flowing through the electrodes and the fusible element therebetween is forced to follow a tortuous path of such configuration that both radial and tangential applied to the fusible element so that the latter is not only'expelled from between the electrodes upon melting and disintegration thereof under an excessive high-current load, but extinguishment of an are between the electrodes established upon interruption of the current is facilitated by virtue of spinning of such are at a speed to prevent dwelling thereof at any one point on the edges of the sidewalls of the electrodes. In thisconnection, an additional important object of the invention is to provide a power fuse as described wherein the slots in the electrodes can take various shapes including 'J-shaped stretches in the base segments of the electrodes leading into either straight stretches in the sidewall portions thereof which are parallel with a central axis through the electrodes, or angularstretches at an angle with respect to such axis and which are aligned or offset relatively, to thereby permit construction of power fuses of varying interrupting capabilities which most effectively and efficiently meet a particularoperational and load specification.

In the drawings: FIG. I is across-sectional view of a preferred form of the power fuse of this invention with the cup-shaped electrodes and leads therefor being shown in elevation; 7

FIG. 2 is an enlarged, fragmentary view showing the preferred electrodes and fusible elements therebetween in perspective;

FIG. 3 is a top plan view of the upper electrode on the same scale as FIG. 2 and containing diagrammatic vector representations of forces on the fusible elements through the fuse;

FIG. 4 is an essentially diagrammatic, cross-sectional representation of the, electrodes on a scale illustrating the preferred spacing therebetween in relationship to the distance from the outer edge of the sidewall of each electrode to the center of the disclike base segment thereof;

FIG 5 is an enlarged cross-sectional, detail view taken along line 5--5 of FIG. 2 illustrating a preferred manner of securing each of the fusible elementsto a respective electrode;

FIG. 6 is a plan view on the same scale as FIG. 3 and illustrating a modified form of the power fuse wherein one electrode has been rotated 30 with respect to the other electrode;

FIG. 7 is a side elevational view of the electrode orientation illustrated in FIG. 6;

FIG. 8 is a side elevational view on the same scale as FIGS. 6 and 7 of a further modified form of the power fuse of this inventioN wherein the electrodes are provided with inclined slots in the sidewall portions thereof each extending through an arc of 120 with the sidewall slots of the upper electrode inclined in a direction opposite to the inclination of the sidewall slots in the lower electrode and angularly displaced one with respect to the other 120"; and

FIG. 9 is a plan view on a reduced scale of the lower electrode of the power fuse showing another modified construction thereof wherein the fusible elements interconnect separate components of the electrode and spaced 120 apart.

Referring to FIG. 1, the fuse 10 has a cylindrical housing 11 made up of mating cylinders 12 and 13 of insulating material. The housing It has cup-shaped, circular, metallic end plates 14 and 16 secured to cylinders 12 and 13 respectively in closing relationship thereto to present a cylindrical chamber 18 therewithin. A cylindrical metallic shield 19 is provided within chamber 18 and is connected to an intermediate circumferentially extending, outwardly projecting flange 22 which is received between proximal end margins of cylinders 12 and 13. The chamber 18 is evacuated after assembly of the fuse, an evacuation tube 20 extending through the end plate 16 being provided for this purpose. A vacuum in chamber 18 on the orderfof 10" to I0 torr is established, and the chamber 18 is then sealed such as by pinching the tube 20 shut as illustrated. Flange 22 serves as a convenient conductive member for electrical check out or the vacuum chamber 18 and parts thereof located therewithin.

A pair of upper and lower, cup-shaped electrodes 24 and 240 are disposed in chamber 18 in spaced, axially aligned relation ship to each other. The two electrodes 24 and 24a are idehtlcal iii configuration with one being inverted with respect to the other. Therefore, it will be understood that corresponding features of the two electrodes are designated by the same as current flows reference numerals with the addition of the a" notation with reference to the lower electrode 24a.

The disclike base segments 25 and 25a of electrodes 24 and 24a have central regions 26 and 26a to which a pair of solid copper leads 28 and 28a are joined both mechanically and electrically at their respective lower and upper ends by conventional means such as silver solder or screws. The lead 28 is connected to a high-voltage line (not shown) to be protected by the fuse. The lead 280 from the lower electrode 24a ex- ,tends through the end plate 16 and is also connected to the line to place the fuse in series therewith.

Each of the electrodes 24 and 24a is of cup-shaped configuration and provided with cylindrical sidewall portions 27 and 27a integral with the circular base segments 25 and 25a thereof and cooperable therewith to define respective cavities 29 and 290. As is best evident in FIG. 4, the depth of the cavity (B-l-X) in electrodes 24 and 24a is atleast as great and preferably greater than the distance from the interior edge of sidewall portion 30 to the central axis of rod electrodes 28 and 28a (distance B in FIG. 4). The outer margins of edge sections 30 and 30a are transversely rounded as shown in FIGS. 2 and 4 to eliminate sharp edges which could serve as are propagatOl'S.

Slot means including stretches made up of three generally J shaped longitudinally arcuate slots 31, 32, and 33 and 31a, 32a and 33a are provided in the base segments of electrodes 24 and 24a respectively, and extend from the central regions 26 and 26a radially and tangentially outwardly to the circumferential periphery of the respective base segments. The inner and outer terminations of the three slots 31, 32 and 33 as well as slots 31a, 32a and 33a are angularly spaced at intervals of 120, and adjacent slots partially angularly overlap each other as is clear in FIG. 3.

It is to be particularly noted that the slots 31, 32, 33 as well as slots 31a, 32a and 33a have relatively straight outermost segments which approach parallelism with tangents to the sidewall portions 27 and 27a at the point of termination of the respective slots. Similarly, the innermost segments of the slot are of generally linear configuration and extend in generally tangential relationship to the leads 28 and 280 respectively. The zone of merger of each straight slot segment into the adjacent slot segment is preferably of relatively uniform radius defining a part of a circle extending to an adjacent portion of wall portions 27 and 27a.

Linear slots 31, 32'and 33 as well as 3l'a, 32'a and 33-a are also provided in sidewall portions 27 and 27a of electrodes 24.and 240 with each of such linear slots extending from the outer end of a respective slot 31-33 and 3la-33a in perpendicular relationship thereto to the edge sections 30 and 30a of the electrodes in parallelism with the central axis 40 of the electrode assembly extending longitudinally of leads 28 and 28a. The slots 31'-33' and 31'a-33'a are preferably of the same width as slots 31-33 and 31a-33a. The slots in electrodes 24 and 24a thus divide each of the latter into three separate components which are integrally interconnected only adjacent the regions 26 and 26a of base segments 25 and 25a. In a preferred embodiment of the invention, the electrodes 24 and 24a have an effective cross-sectional dimension of about l inches, are about 78 inch high, have a base segment about V4 inch in thickness, are provided with a sidewall portion of 5/32 inch thickness, have slots about l/IO inch and are spaced apart relatively at least about inch.

Three fusible, rodlike elements 34, 36 and 38, which may be of copper or other suitable conductive composition, span the sidewall portions 27 and 27a of electrodes 24 and 24a respectively and are disposed intermediate the opposed cylindrical surfaces thereof between the outer terminal extremities of slots 32 and 33, and slots 32a and 33a. The elements 34, 36 and 38 are equally angularly spaced about central axis 40 of the electrodes 24 and 24a defined by their geometric centers with element 38 somewhat closer to slots 33 and 33'a than the spacing of element 34 from slots 32' and 32'a. The

' sidewall portions of the components of electrodes 24 and 244 which support elements 34, 36 and 38 are each provided with aligned bores 42 in the upper and lower electrodes for receiving respective fusible elements. To effect both an electrical and a mechanical connection between elements 34, 36 and 38 and electrodes 24 and 24a, the sidewall portions 27 are crimped around the tips of the upper and lower end portion of elements 34, 36 and 38 as is best evident from FIG. 5.

Fuse structure 10 is especially adapted for the protection of altemating-current power lines having voltages on the order of 600 volts through the high-voltage range. The leads 28 and 28a are connected to the line to be protected to place the elements 34, 36 and 38 in series with such line. FIG. 3 illustrates the current paths to the three elements 34, 36 and 38 which extend from the central region 26a of the electrode 240 around the slot 33a. Identical current paths also exist between the central region 26 of the upper electrode 24 and the elements 34, 36 and 38, except that the direction of current flow is opposite during a given half cycle of the altemating-current wave.

The current path along electrode 24a to the element 34 is represented at 54 and is a straight line from the arcuate part of the slot 33a to the lower tip of the element 34 where the connection is made to the sidewall portion 27a of electrode 240. The current path to the element 36 is represented at 56 and follows the outer edge of the slot 33a until the latter diverges from a direct line to the element 36, at which point the path 56 follows a straight line from the bend in the slot 30 to the element 36. Similarly, the current path 58 to the third element 38 follows the slot 33a for better than one-half of its length before traversing a straight line to the element 38. It may be appreciated, therefore, that the .I-shaped configuration of the slot 33a forces the current paths 54, 56 and 58 to extend in both radial and tangential directions with respect to the central axis 40 in order to reach the respective elements 34, 36 and 38 are progressively longer in length, as is clear from a study of FIG. 3.

-When a short circuit or overload current flows through the fuse, the paths 54, 56 and 58 are necessarily traversed by the current to cause the current to apply electromagnetic forces to the three elements. The resultant force on the element 34 is represented by the vector R the resultant force on the element 36 is represented by the vector R,, and the resultant force on the element 38 is represented by the vector R Each of these vectors has both radial and tangential force components as is clearly illustrated in the vector diagrams included in Fig. 3. As each element 34, 36 or 38 melts and disintegrates when excessive current such as a short circuit is applied thereto, the presence of the resultant vector R R, or R expels the material residue from such element from between the sidewall portions 27 and 27a of electrodes 24 and 244 by ejection therefrom in a direction toward the shield 19 (Fig. 1). Thus, the residue material from the current-responsive elements is not permitted to remain between or on the electrodes where substantial volatilization thereof could occur when areing across the electrodes is ultimately produced upon severance of all of the elements.

The tangential force components are identified P,, P, and P and serve to spin the arc about the axis 40 to further reduce the volatilization of the fusible elements and also prevent excessive volatilization of the electrode material. This spinning persists until a natural current zero occurs following severance of the three elements. This action will now be explained in greater detail.

Besides the tangential force components P,, P, and P forces of mutual attraction between the elements 34, 36 and 38 are present prior to severance of the elements by the melting thereof. Thus, an attractive force exists between elements 34 and 36, a second attractive force exists between elements 36 and 38, and a third attractive force is in existence between elements 34 and 38. Therefore, the total force on element 34 is the vectorial sum of R (including its tangential component P,) and the mutual forces of attraction between element 34 and elements 36 and 38. It is believed that this total force on element 34 is the greatest total force experienced by any of the elements. This conclusion is reached since, prior to severance ofany element, the forces of mutual attraction on the center element 36 cancel one another, and the resultant mutual attraction force on the element 38 is the vectorial sum of the mutual attraction force between elements 34 and 38 and the mutual attraction force between elements 36 and 38, both of which are essentially in opposition to the force R in contrast to this, the force R and the mutual attraction forces actingonelement34 are vectorially additive, resulting in a higher total force on element 34.

in accordance with the foregoing, it is believed that when the element 34 reaches a plastic state, due to the flow of short circuit or overload current therethrough, this element is severed and caused to disintegrate first because of the higher total force acting thereon in a direction transverse to its length. This increases the currents through the remaining elements 36 and 38. The total force on the element 36 now becomes a vectorial combination of R, and the mutual attraction force between elements 36 and 38; therefore, the element 36 is the next to sever and disintegrate. With element 36 now severed, the entire current must flow through the single remaining element 38, which severs and disintegrates immediately due to the high force of R acting thereon. The severance of all three elements occurs very'rapidly and, if the short circuit condition occurs as the current wave is ascending, complete severance of all elements should be effected prior to the time that the current wave reaches the next natural'current zero, with full interruption of the circuit occurring atthe current zero point.

ln order for interruption to occur, the arc that will be established across the electrodes 24 and 24a at the time of severance of the last element must be extinguished. Due to the presence of the tangential force component P,, the arc is forced to move along the sidewall portions 27 and 27a of the electrodes and is thus spun about the central axis 40. The presence of tangential forces to maintain the arc in motion is assured by the J-shaped configuration of the slots 31, 32 and 33, the latter serving to maintain a tangential driving force on the are at all angular positions thereof to sustain the spinning motion. Therefore, substantial volatilization of the electrode material, as well as the elements 34-38, is precluded since the arc is prevented from dwelling where initially established. The spinning motion of the arc continues until the current zero is reached, whereupon extinguishment of the arc completes the interruption of the circuit. in addition, the provision of cavities 29 and 29a in electrodes 24 and 24a prevents the are from traveling to the center thereof where an equilibrium position would be established tending to prevent extinguishment of the arc. Contributing to this retention of the are on the edge sections 30 and 30a of electrodes 24 and 24a is the fact that since the electrical path B in Fig. 4 is less than the path B .-l-X, (FIG. 4) there is no tendency for the are to move toward the central the central areas of the electrodes.

As may now be appreciated, the material of the electrodes 24 and 24a should, as much as possible, be resistant to volatilization to minimize the generation of gaseous ions during interruption. Annealed copper is suitable as the electrode material and should be baked out at a sufficient temperature to remove occluded gases which could interfere with the interruption of the fuse.

Although three fusible elements 34-38 are illustrated herein, it should be understood that one or a plurality of such elements may be utilized in accordance with the continuous rating desired for a particular fuse application. in this respect, it is noteworthy that the construction of the fuse of the present invention is such that fuses of different ratings may be constructed utilizing the same basic eomponents'without modification, except for the number, size and materialof the fusible elements themselves. The adaptation of elements of difierent diameters to a single-electrode design is best illustrated in FIG. 5, where it may be seen that elements of d ifierent diameters may be inserted into the respective openings therefor in the electrodes. The opening 42 there illustrated is desirably of a diameter greater than the maximum diameter of the fusible elements to be utilized.

In the modified power fuse illustrated in FIGS. 6 and 7 of the drawings, the electrodes 124 and 1244 shown are of identical construction to electrodes 24 and 240 except that upper electrode 124 has been rotated 30 relative to lower electrode 124a while element 134 between edge sections 130 and 130a of sidewall portions 127 and 127a is retained in a position parallel with central axis 140 through leads 128 and 1280. The slots in electrode 124 and 124a, are of the same shape and relative disposition as the slots in electrodes 24 and 24a except for being angularly offset 30 relatively. This angular offset relationship balances or distributes the forces on the arc to sustain the speed of arc movement until extinguishment. Although only one fusible element 134 is illustrated in FIGS. 6 and 7 it is to be understood that two, three or more elements may be provided as desired for the reasons explained above.

Under certain other types of power requirements and load conditions, cup-shaped electrodes having three slots therein of the configurations illustrated in FIG. 8 give improved results over electrodes 24 and 24a or 124 and 124a. In this instance, the slots in the sidewall portions 227 and 227a of electrodes 224 and 2240 extend at an angle of about 30 across wall portions 227 and 2270 instead of being parallel to the central axis of leads 228 and 2280. As is apparent from FIG. 8, each of the slots 232' and 232'a are aligned along the axis of the fuse assembly and extend from the slots 232 and 2320 respectively of the base segments 225 and 2250 of the electrodes 224 and 224a around the perimeter thereof a total angular distance of In addition, the slots in opposed electrodes are inclined in opposite directions so that the lower electrode 2240 is a mirror image of the upper electrode 224. Although not illustrated, it is to be understood that the slots in the base segments of electrodes 224 and 224a are of the same configuration as slots 31-33 and 3la-33a in electrodes 24 and 240.

Figure 9 illustrates. another modified form of power fuse embodying the principles of this invention wherein the fusible elements 434, 436 and. 438 corresponding to elements 34, 46 and 38 respectively are located in equally spaced relationship 120 apart around the sidewall portion 427a of the electrode 424a, rather than being mounted on one of the divided components thereof as is the case of the electrode construction of FIGS. 1-3. In this instance, the elements 434, 436 and 438 tend to melt and disintegrate substantially simultaneously rather than in serial order as is the case when all elements are positioned in proximal relationship about 30 apart as previouslydescribed.

in the case of three elements located [20 with respect to each other, there results a lesser amount of conductive element material in any given location. The equal dispersion of volatilized conductive material reduces the material density in various arc locations thereby aiding with are extinction. This also applies for two or more than three elements.

Regardless of the particular slot arrangement utilized in the cup-shaped electrodes of this invention, it is important that the radial and tangential force components produced as a result of the slotted configuration have sufi'rcient magnitude to execute the element-ejecting and arc-spinning functions discussed above. Otherwise, the problem of excessive volatilization becomes acute, and the fuse would not be suited to the high-voltage, high-power applications for which the present invention is particularly adapted. Although the advantageous features of the fuse are useful at voltages as low as 600 volts, special need for the invention is particularly experienced at line voltages on the order 5,000 volts and above.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. A power fuse comprising:

housing structure having an evacuated chamber therein;

a pair of spaced, cup-shaped electrodes in said chamber, each electrode being provided with a base segment and a sidewall portion extending outwardly therefrom to present an outer edge section spaced from the base segment of the electrode, said electrodes being positioned in the chamber with the edge sections thereof in directly opposed, spaced, facing relationship;

at least one fusible, current-responsive element extending between the edge sections of said electrodes and electrically interconnecting the latter; and

means for electrically connecting said electrodes with a current-carrying line to interpose said element in series with said line,

at least one of said electrodes having slot means in the base segment and the sidewall portion thereof of a configuration to cause current flowing between said electrodes through the element to apply a force thereto in a direction to both a. expel the element from the space between the edge sections of the electrodes upon melting and disintegration of the element under short circuit current conditions and attendant establishment of an arc across the edge sections of the electrodes, and

b. effect movement of the are along the edge sections of the electrodes in spaced relationship from the base segments thereof to prevent the arc from dwelling where initially established or at any one point on the electrodes.

2. A power fuse as set forth in claim 1,

the base segment of each electrode comprising a disclike member and the sidewall portion of the electrode projecting from the peripheryof the disclike member in circumscribing relationship thereto.

3. A power fuse as set forth in claim 2,

the base segment of each electrode being generally circular and the sidewall portion thereof being of generally cylindrical configuration.

4. A power fuse as set forth in claim 2,

each of said electrodes being provided with slot means therein comprising at least one slot having a first stretch extending through the sidewall portion of each electrode from the edge section to the base segment thereof, and a second arcuate stretch extending inwardly of the base segment toward the center thereof.

5. A power fuse as set forth in claim 4,

said second stretch of the slot being of J-shaped configuration with the part thereof extending toward the periphery of the base segment progressively approaching tangential relationship to said periphery.

6. A power fuse as set forth in claim 4,

the first stretch of each slot means in said electrodes being in generally parallel relationship to a central axis extending through the electrodes.

7. A power fuse as set forth in claim 4,

each of said electrodes being provided with a plurality of said slots therein.

8. A power fuse as set forth in claim 7,

each of said electrodes being provided with three of said slots therein, the first stretches of said slots being spaced apart 120 around the perimeter of the sidewall portion of said electrode.

7 9. A power fuse as set forth in claim 1,

said electrodes each having a depth of cavity defined by said sidewall portion thereof at least as great as the distance from the edge section of each electrode to a central axis through said base segments thereof.

10. A power fuse as set forth in claim 4,

the slot means in one electrode being offset angularly of the electrodes with respect to the slot means in the other electrode of said pair thereof.

1 l. A power fuse as set forth in claim 10,

the slot means in said one electrode being offset about 30 angularly of the electrodes with respect to the slot means in said other electrode.

12. A power fuse as set forth in claim 4,

said first stretch of the slot means in each electrode being disposed at an angle with respect to a central axis extending through the electrodes.

13. A power fuse as set forth in claim 12,

said first stretch of the slot means in each electrode extending through an angular distance of about 14. A power fuse as set forth in claim 12,

said angular first stretches of the slot means in opposed electrodes being inclined relatively in opposite directions and each extending through an angular distance of about 120.

15. A power fuse as set forth in claim 12,

said angular first stretch of the slot means in each electrode extending from the face of the base segment thereof proximal to the sidewall portion, to the edge section of the electrode.

16. A power fuse as set forth in claim 12,

said electrodes each being provided with three of said slot means therein and each comprising a mirror image of the other with the first stretches thereof being inclined in opposite directions and each extending through in angular distance of about 120.

17. The power fuse as claimed in claim 1,

said element being rodlike and having a diameter selected in accordance with the desired continuous current rating of the fuse.

18. The power fuse as claimed in claim 1,

each of said base segments of the electrodes having an outer periphery,

said connecting means being connected to a region of each electrode disposed centrally with respect to the periphery of said base segment thereof,

the central regions of said electrodes being aligned to define an axis extending between the electrodes through said regions,

said element spanning said electrodes between the edge portions thereof in spaced relationship to said central regrons,

said slot means being configured and positioned to cause the force produced components to be directed radially outwardly of said axis and tangentially thereof respectively, whereby the force effects the expulsion of the element upon melting and disintegration thereof and the tangential component thereof imparts said movement to the arc and spins the latter about said axis.

19. The power fuse as claimed in claim 18,

each of said electrodes having a hollow bore in the sidewall portion thereof for receiving a respective end of said element,

the sidewall portion of each electrode being crimped around the end of the element received therein.

20. The power fuse as claimed in clam l8;

and a shield radially spaced from said axis and disposed in surrounding relationship to said electrodes between the latter and said housing.

21. The power fuse as claimed in claim 1,

a plurality of fusible, current-responsive elements extending between the edge sections of said electrodes and located in angularly spaced relationship, said element electrically interconnecting the edge sections of the electrodes.

22. The power fuse as claimed in claim 21,

said electrodes each being provided with a plurality of said slot means therein dividing the base segment and said sidewall portion thereof into separate components interconnected only by a central part of a respective base segment,

there being at least one element interconnecting each of the opposed components of said electrodes.

23. The power fuse as claimed in claim 21,

said electrodes each being provided with a plurality of slot means therein dividing the base segment and said sidewall portion thereof into separate components interconnected only by a central part of a respective base segment, 

1. A power fuse comprising: housing structure having an evacuated chamber therein; a pair of spaced, cup-shaped electrodes in said chamber, each electrode being provided with a base segment and a sidewall portion extending outwardly therefrom to present an outer edge section spaced from the base segment of the electrode, said electrodes being positioned in the chamber with the edge sections thereof in directly opposed, spaced, facing relationship; at least one fusible, current-responsive element extending between the edge sections of said electrodes and electrically interconnecting the latter; and means for electrically connecting said electrodes with a current-carrying line to interpose said element in series with said line, at least one of said electrodes having slot means in the base segment and the sidewall portion thereof of a configuration to cause current flowing between said electrodes through the element to apply a force thereto in a direction to both a. expel the element from the space between the edge sections of the electrodes upon melting and disintegration of the element under short circuit current conditions and attendant establishment of an arc across the edge sections of the electrodes, and b. effect movement of the arc along the edge sections of the electrodes in spaced relationship from the base segments thereof to prevent the arc from dwelling where initially established or at any one point on the electrodes.
 2. A power fuse as set forth in claim 1, the base segment of each electrode comprising a disclike member and the sidewall portion of the electrode projecting from the periphery of the disclike member in circumscribing relationship thereto.
 3. A power fuse as set forth in claim 2, the base segment of each electrode being generally circular and the sidewall portion thereof being of generally cylindrical configuration.
 4. A power fuse as set forth in claim 2, each of said electrodes being provided with slot means therein comprising at least one slot having a first stretch extending through the sidewall portion of each electrode from the edge section to the base segment thereof, and a second arcuate stretch extending inwardly of the base segment toward the center thereof.
 5. A power fuse as set forth in claim 4, said second stretch of the slot being of J-shaped configuration with the part thereof extending toward the periphery of the base segment progressively approaching tangential relationship to said periphery.
 6. A power fuse as set forth in claim 4, the first stretch of each slot means in said electrodes being in generally parallel relationship to a central axis extending through the electrodes.
 7. A power fuse as set forth in claim 4, each of said electrodes being provided with a plurality of said slots therein.
 8. A power fuse as set forth in claim 7, each of said electrodes being provided with three of said slots therein, the first stretches of said slots being spaced apart 120* around the perimeter of the sidewall portion of said electrode.
 9. A power fuse as set forth in claim 1, said electrodes each having a depth of cavity defined by said sidewall portion thereof at least as great as the distance from the edge section of each electrode to a central axis throUgh said base segments thereof.
 10. A power fuse as set forth in claim 4, the slot means in one electrode being offset angularly of the electrodes with respect to the slot means in the other electrode of said pair thereof.
 11. A power fuse as set forth in claim 10, the slot means in said one electrode being offset about 30* angularly of the electrodes with respect to the slot means in said other electrode.
 12. A power fuse as set forth in claim 4, said first stretch of the slot means in each electrode being disposed at an angle with respect to a central axis extending through the electrodes.
 13. A power fuse as set forth in claim 12, said first stretch of the slot means in each electrode extending through an angular distance of about 120* .
 14. A power fuse as set forth in claim 12, said angular first stretches of the slot means in opposed electrodes being inclined relatively in opposite directions and each extending through an angular distance of about 120* .
 15. A power fuse as set forth in claim 12, said angular first stretch of the slot means in each electrode extending from the face of the base segment thereof proximal to the sidewall portion, to the edge section of the electrode.
 16. A power fuse as set forth in claim 12, said electrodes each being provided with three of said slot means therein and each comprising a mirror image of the other with the first stretches thereof being inclined in opposite directions and each extending through in angular distance of about 120* .
 17. The power fuse as claimed in claim 1, said element being rodlike and having a diameter selected in accordance with the desired continuous current rating of the fuse.
 18. The power fuse as claimed in claim 1, each of said base segments of the electrodes having an outer periphery, said connecting means being connected to a region of each electrode disposed centrally with respect to the periphery of said base segment thereof, the central regions of said electrodes being aligned to define an axis extending between the electrodes through said regions, said element spanning said electrodes between the edge portions thereof in spaced relationship to said central regions, said slot means being configured and positioned to cause the force produced components to be directed radially outwardly of said axis and tangentially thereof respectively, whereby the force effects the expulsion of the element upon melting and disintegration thereof and the tangential component thereof imparts said movement to the arc and spins the latter about said axis.
 19. The power fuse as claimed in claim 18, each of said electrodes having a hollow bore in the sidewall portion thereof for receiving a respective end of said element, the sidewall portion of each electrode being crimped around the end of the element received therein.
 20. The power fuse as claimed in clam 18; and a shield radially spaced from said axis and disposed in surrounding relationship to said electrodes between the latter and said housing.
 21. The power fuse as claimed in claim 1, a plurality of fusible, current-responsive elements extending between the edge sections of said electrodes and located in angularly spaced relationship, said element electrically interconnecting the edge sections of the electrodes.
 22. The power fuse as claimed in claim 21, said electrodes each being provided with a plurality of said slot means therein dividing the base segment and said sidewall portion thereof into separate components interconnected only by a central part of a respective base segment, there being at least one element interconnecting each of the opposed components of said electrodes.
 23. The power fuse as claimed in claim 21, said electrodes each being provided with a plurality of slot means therein dividing the base segment and said sidewall portion thereof into separate comPonents interconnected only by a central part of a respective base segment, said plurality of fusible elements interconnecting one pair of opposed components of said pair of electrodes. 